JPH05295561A - Improvement for applying tellurium-containing coating film on metal surface using cyclodeoxtrin/tellurium composition - Google Patents

Abstract

PURPOSE: To provide a modified tellurium compsn. for applying a uniform durable tellurium coating film on a metal surface by constituting the compsn. by incorporating therein water, phosphate ions, tellurium ions and cyclodextrin based on a specific weight as a reference.

CONSTITUTION: Water, phosphate ions of about 0.1 to about 400000 ppm, tellurium ions of about 0.1 to about 100000 ppm and cyclodextrin of about 0.1 to about 100000 ppm based on the weight of water as a reference are incorporated in the compsn. for applying the coating film on the metal surface. The pH value of this compsn. is adjusted to a pH value in the central range. Cyclodextrin is defined as β cyclodextrin. Thus, a paint being subsequently applied and the appearance of the other coating film are improved.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improved tellurium compositions and methods for applying tellurium coatings to metal surfaces. These coating compositions are characterized by the presence of tellurium and cyclodextrin solubilizers.

As used herein, the term "coating" refers to a substance that adheres to the surface of a metal that is chemically different from the metal itself. A particular example of a coating is a phosphate-based conversion coating. Such coatings are produced by chemical interactions between the phosphate-containing coating composition and the metal substrate being treated.

Conversion coatings are used to enhance the corrosion resistance of treated metal surfaces and to improve the adhesion of paints and other coatings to these surfaces. As practiced in the art, conversion coatings are commonly applied to metal surfaces as iron phosphate, zinc phosphate, or manganese phosphate. For example, a conversion coating may be used to coat metal surfaces with phosphate sources, acids,
And a composition containing a promoter. Common accelerators used for this include molybdenum, vanadium, nickel, and tungsten salts.

Prior to applying the conversion coating, the metal surface to be treated is generally cleaned to remove oils, grease, and other impurities. These impurities act as a mechanical barrier to the conversion coating composition or solution and interfere with or completely prevent adhesion of the conversion coating to the treated metal surface.

After cleaning, the metal surface is typically contacted with a conversion coating solution containing an acid, a phosphate source, an oxidizer, and a promoter. The surface is then typically washed with water to remove unreacted reagent and phosphate. Prior to painting, the chromate, nitrate, or pickling agent is finally applied to the surface being treated.

[0006]

There are some inherent drawbacks to conventional conversion coating processes such as the iron phosphate coating process.
The key to these is that the iron phosphate method generally produces a lower corrosion resistant coating than the zinc phosphate coating method. Since the zinc phosphate process is generally more complex to use, costly and environmentally undesirable, there has been a long-standing need in the industry for a convenient and inexpensive way to provide a corrosion resistant conversion film. .. This need is met by the present methods and compositions.

Accordingly, it is an object of the present invention to provide an improved tellurium composition and method for providing a uniform, durable tellurium coating on a metal surface to impart corrosion resistance to the substrate being treated. This object is achieved by using a tellurium coating composition containing a tellurium ion source and a solubilizer selected from the group consisting of cyclodextrins to form a coating characterized by the presence of tellurium. The present invention may treat any metal surface including, but not limited to, plated surfaces, stainless steel surfaces, mild steel surfaces, and aluminum surfaces.

This and other objects of the invention are achieved by the compositions and methods disclosed herein. The present coating compositions and methods allow for the application of uniform tellurium coatings to metal surfaces, especially in the central pH range. The method is
It can be used at any temperature up to the boiling point and the resulting coating provides the substrate with corrosion resistance. The coating further improves the appearance of coatings and other coatings that are typically subsequently applied to treated metal surfaces.

[0009]

BACKGROUND OF THE INVENTION According to MERCK INDEX 10th edition, tellurium is the reagent which produces a black finish on silverware.

US Pat. No. 4,713,121 discloses phosphate conversion coatings containing primary and secondary divalent metal elements such as cobalt and zinc.

US Pat. No. 4,391,855 discloses a coating method using a composition containing a powdered metal dispersed in a binder as a corrosion inhibitor.

US Pat. No. 4,149,909 discloses chlorates and bromates as promoters and hydroxylamine sulphate as reducing agents in phosphating compositions used to produce iron phosphate coatings. Disclose the use.

US Pat. No. 4,595,424 discloses a phosphate coating for use on a zinc surface containing a phosphate ion source, a zinc and / or manganese ion source, and a complex of fluoride ions. A solution is disclosed.

US Pat. No. 4,634,295 shows the corrosion resistance of metal substrates which requires the application of direct current to a prezinc phosphated metal surface in an acidic solution containing zinc, phosphate and chloride ions. A method for improving is disclosed.

Co-pending US Patent Application No. 361,08
No. 7 discloses tellurium compositions and methods for applying tellurium compositions to metal surfaces. Co-pending US Patent Application No. 722,740 discloses the use of cyclodextrins to solubilize tellurium.

[0016]

SUMMARY OF THE INVENTION The present invention is an improved tellurium coating composition and an improved method for applying a tellurium coating to a metal surface selected from the group consisting of a tellurium ion source and a cyclodextrin. Compositions and methods characterized by the use and / or presence of tellurium solubilizers.

The present invention comprises the following: A) a metal surface comprising: a) water; b) about 0.1 to about 100,000 based on the weight of a).
0 ppm tellurium ion; c) about 0.1 to about 100,000 based on the weight of a).
0 ppm cyclodextrin; d) optionally about 0.1 to about 40, based on the weight of a).
50,000 ppm phosphate ions; and e) optionally about 0.1 to about 20 based on the weight of a).
Shown is a method for applying a coating to a metal surface comprising contacting with an effective amount of an aqueous coating composition containing 0. 000 ppm oxidizer; and B) optionally washing and drying the metal surface.

With respect to the present method, the term "effective amount" refers to the metal surface and coating composition to be coated within a suitable time to bond the coating characterized by the presence of tellurium to the metal surface being treated. 1 illustrates the amount of coating composition required to provide a homogenous bond between the.

In the aqueous composition of the present invention, cyclodextrin is used as a tellurium solubilizer. Cyclodextrins solubilize tellurium over the entire pH range, as disclosed in co-pending application No. 722,740. Thus, coating of substrates with tellurium coating compositions in the central pH range is possible. Thus, the coating composition can be formulated at a pH at which tellurium is soluble, and the pH of the coating composition is adjusted to the central pH range so that the coating can be applied more conveniently and safely. As used herein, the term "central pH range" refers to about 2.5 to about 1.
It shows 1.0, preferably about 3.0 to about 9.0.

The tellurium ion source provides the tellurium to be present in the coating formed on the substrate. Optionally, a phosphate ion source and / or an oxidant may be used. Phosphates and oxidants facilitate pretreatment of metal substrates. There may be one or more acids present. The acid is believed to promote the bonding of the tellurium coating to the substrate. Hydrochloric acid and sulfuric acid are preferred.

In addition, an effective amount of surfactant may be added for cleaning, infiltration and / or wetting, and an effective amount of fluoride source may be added for use on plating or aluminum surfaces. Other conventional additives used in processing compositions may be added, such as chelating agents.

The present invention further comprises the following: a) water; b) about 0.1 to about 400000, based on the weight of a).
0 ppm of phosphate ions; c) about 0.1 to about 100,000 based on the weight of a).
0 ppm tellurium ion source; d) about 0.1 to about 100,000 based on the weight of a).
1 shows a composition containing 0 ppm cyclodextrin.

The composition provides a coating characterized by the presence of tellurium. These coatings generally enhance the resistance of treated metal surfaces to corrosion and improve the adhesion of paints and other coatings to these surfaces. Before applying this coating,
Generally, the surface to be coated is treated with chemical additives, mechanical abrasion,
And several washes to clean. Conventional conversion coating compositions, such as iron phosphate coating compositions, generally contain metals such as molybdenum, vanadium, nickel, and / or tungsten salts to facilitate the coating process and provide an adherent coating.

An essential ingredient of the composition is a cyclodextrin solubilizer. Any cyclodextrin can be used. Cyclodextrins are generally (C ₆ H ₁₀ O ₅ ) _x
(Where x is a minimum of 6). Preferred cyclodextrins are α- (x = 6), β- (x =
7), and γ- (x = 8) cyclodextrin,
Most preferred is β-cyclodextrin. Cyclodextrin is available from Amaizo Corporation
on the market. Cyclodextrin solubilizes tellurium ions over a wide pH range, giving a central pH.
Allows the application of tellurium coatings in a range. In the absence of cyclodextrin or other solubilizer, tellurium is generally insoluble at pH below about 2.5 and above about 11.0.

Optionally, any source of phosphate ions may be used in the present compositions and methods, including phosphoric acid and phosphate salts, such as the ammonium, potassium, lithium, or sodium salts of orthophosphoric acid or pyrophosphate. However, it is not limited to these. For example, suitable phosphates include monopotassium orthophosphate, dipotassium orthophosphate,
Tripotassium orthophosphate, monosodium orthophosphate, disodium orthophosphate, trisodium orthophosphate, hemisodium orthophosphate, monoammonium orthophosphate, diammonium orthophosphate, triammonium orthophosphate, lithium ortholine Acid salts, sodium tripolyphosphate, tetrasodium pyrophosphate, disodium pyrophosphate, sodium hexametaphosphate, sodium ammonium pyrophosphate, sodium octametaphosphate, and sodium heptametaphosphate, but these include Not limited. Preferred sources of phosphate ions are trimetaphosphate, orthophosphate, hexametaphosphate, and tripolyphosphate. The most preferred phosphate ion source is sodium trimetaphosphate. The coating composition contains from about 0.1 to about 400,000 ppm active phosphate ions, based on the total water content of the coating composition. Preferably, these compositions contain about 1 to about 200,000 ppm phosphate ions. Phosphate ions help retain the solubility of tellurium. Phosphates also act as chelating and sludge reducing agents.

The coating composition may optionally contain from about 0.1 to about 200,000 ppm of oxidizer, based on the weight of water in the coating composition. Preferably, they are about 1.0
~ About 100,000 ppm oxidizer. Any oxidizing agent can be used. The preferred oxidant is selected from the group consisting of chlorates and nitrates. The most preferred oxidant is
Sodium chlorate and sodium nitrate.

The coating composition contains at least about 0.1 ppm active tellurium ion, based on the weight of water in the coating composition, and has an upper limit set by tellurium solubility. Preferably about 0.1 to about 100,000 pp
m, most preferably about 1 to about 50,000 ppm tellurium ion is present. Any source of tellurium ions can be used. Preferred tellurium ion sources are oxides of tellurium and salts of telluric acid or tellurite. The most preferred sources of tellurium ions are tellurium oxide and salts of telluric acid.

The balance of the composition is water, but other agents may be used. For example, acids, surfactants, fluoride ion sources, and chelating agents are also desirable.

An effective amount of heavy metal catalyst may be used in the composition of the present invention. Such catalysts include, but are not limited to, compounds of metals such as vanadium, titanium, zirconium, tungsten, and molybdenum. Preferred catalysts are sodium molybdate and ammonium metavanadate. Other promoters, such as acid soluble salts of nickel, cobalt, magnesium, sodium, and calcium, may be used in the compositions of the present invention in combination with, or instead of, these heavy metal catalysts. Common anions for these salts include nitrates, nitrites, and chlorates,
It is not limited to these.

An effective amount of chelating agent may optionally be used in the present invention. Such agents include thiourea, ethylenediaminetetraacetic acid, and nitrilotetraacetic acid,
It is not limited to these. A preferred chelating agent is ethylenediaminetetraacetic acid (hereinafter EDTA). The EDTA component of the composition is of any suitable grade. For example, a commercially available solution that is 39% by weight may be used.
It should be noted that certain acids such as citric acid and EDTA are well known as chelating agents.

The composition of the present invention must be in contact with the metal being treated for an effective amount of time. As used herein, the term "effective amount of time" means that the composition is in contact with the metal surface being treated so as to produce a uniform adherent coating,
It means the amount of time required to react. Preferably,
The contact time is about 1 to 60 minutes, more preferably about 1 to 3 minutes.
0 minutes, most preferably about 1-5 minutes. Contact between the coating composition and the metal surface is provided by any known method including, but not limited to, spraying and dipping. The working temperature does not appear to be important, but the practical upper limit is the boiling point of the aqueous coating composition. However, the preferred contact temperature is less than about 49 ° C.

Preferred compositions include: wt% (based on activity) α-cyclodextrin 2-20 phosphate ion source 1-20 oxidant 0.5-10 tellurium 0.01-3. Water Balance Optionally, the compositions of the present invention may contain about 0.1-5% by weight heavy metal catalyst, and about 0.1-10% by weight chelating agent. In addition, at least 0.1% by weight, preferably about 0.1 to about 10% by weight fluoroborate compound may be used to provide fluoride ions for etching the metal surface during processing.

The compositions of the present invention may be prepared in a mixing vessel by conventional mixing or compounding methods. It is desirable to stir. The order of addition is not believed to be important. However, the cyclodextrin and tellurium ion sources are
Generally, it should be added before any pH adjustment steps.

The composition of the present invention may be applied to the metal surface by any known method including, but not limited to, spraying and dipping. The coating composition may then be washed and dried to form a coating.

The methods described herein include other methods conventionally used in preparing metal surfaces for painting, including sealing the coated metal surface with a chromium or non-chromium based material. A step may follow, or may further include the step.

[0036]

The following examples further demonstrate the present invention. This example is not intended to limit the invention in any way.

Weight% of Tellurium-based Phosphating Agent Component Composition with Cyclodextrin Water 83.72 Sodium Hydroxide (50%) 8.00 Tellurium Dioxide 0.48 β-Cyclodextrin 2.4 Sodium Trimetaphosphate 10 .8 The above ingredients were added in the order listed. As a result, pH 1
This gave 2.63 of a clear, stable solution. The pH was then adjusted to 11.0 with HCl, but the solution was still clear.

Claims (8)

[Claims] 1. The following: a) water; b) about 0.1 to about 400000, based on the weight of a).
0 ppm of phosphate ions; c) about 0.1 to about 100,000 based on the weight of a).
0 ppm tellurium ion; d) about 0.1 to about 100,000 based on the weight of a).
A composition for applying a coating to a metal surface containing 0 ppm of cyclodextrin. 2. A composition according to claim 1, wherein the pH of the composition is adjusted to the central pH range. 3. The composition according to claim 1, wherein the cyclodextrin is β cyclodextrin. 4. The composition according to claim 2, wherein the cyclodextrin is β cyclodextrin. 5. The following: A) a metal surface comprising: a) water; b) about 0.1 to about 100,000 based on the weight of a).
0 ppm tellurium ion; c) about 0.1 to about 100,000 based on the weight of a).
0 ppm cyclodextrin; d) optionally about 0.1 to about 40, based on the weight of a).
A method for applying a coating to a metal surface comprising contacting with an effective amount of an aqueous coating composition containing 50,000 ppm phosphate ions; and B) optionally cleaning and drying the metal surface. .. 6. The method of claim 5, wherein the composition has a central pH range. 7. The composition according to claim 5, wherein the cyclodextrin is β cyclodextrin. 8. The composition according to claim 6, wherein the cyclodextrin is β cyclodextrin.